1. Field of the Invention
The present invention relates to an ultrasound diagnostic apparatus that performs ultrasound diagnosis using a capacitive micromachined ultrasound transducer.
2. Description of the Related Art
In recent years, the development of ultrasound devices using a capacitive micromachined ultrasound transducer (abbreviated as “C-MUT”), which is different from a piezoelectric transducer, as an ultrasound transducer has been advanced.
In the C-MUT, a vacuum space region is provided between upper and lower electrodes, and a DC bias voltage and a transmission signal or an ultrasound transmission signal are applied to the upper electrode to send ultrasound out toward a site to be examined, and ultrasound returned as a result of reflection is received by an upper film, converted into an ultrasound echo signal (referred to as “ultrasound reception signal” or simply as “reception signal”) as a converted electric signal, and used for ultrasound examination or diagnosis.
The transmission signal transmitted to the C-MUT and the reception signal received in the C-MUT are conveyed via respective cables, and here, the problem of an impedance mismatch may arise between the cables and capacitances the C-MUT has, resulting in a decrease in transmitting/receiving sensitivity.
More specifically, reflection of the transmission signal due to an impedance mismatch causes distortion of the waveform of the transmission signal, a decrease in level of a transmission signal that can actually be applied to the C-MUT or superimposition of a waveform arising from the mismatch on the received reception signal, resulting in a decrease in receiving sensitivity and/or S/N ratio.
Addressing such phenomena, the related art in Japanese Patent No. 4575372 clearly indicates including impedance converting means for converting an output of a transducer element so as to have a low impedance for electrical impedance matching with an impedance of a cable, in the vicinity of the transducer element, for prevention of a decrease in receiving sensitivity.
In the above related art, a same route is provided for transmission and reception, and in particular, focusing on a received signal output, the impedance converting means is provided.